Highly reliable low-latency communication is a basic requirement of many industrial control and factory automation applications. Historically, wired communication served this sector due to the ultrahigh reliability of its dedicated infrastructure but unfortunately at an exorbitant cost of installation and maintenance. In recent years, wireless technologies, however, matured to meet the performance standards by incorporating many novel mechanisms such as Time Synchronized Channel Hopping (TSCH).
TSCH achieves improved communication reliability via channel hopping and avoids external interference operating at the same frequency band. Channel hopping helps to spread the risk of collisions by periodically switching the channel over which transmissions are made. TSCH also maintains low radio duty cycle and low energy consumption by synchronizing network nodes.
A notable example is IEEE 802.15.4, a de-facto standard for wireless personal area networks, which has recently adopted TSCH in its IEEE 802.15.4e MAC. Thanks to its channel and spatial diversity, an unprecedented reliability can be achieved but not without a scheduling mechanism that can avoid conflicts by precisely scheduling multiple wireless transmissions occurring at same time, frequency or spatial proximity.
The Internet Protocol version 6 over the TSCH MAC (6TiSCH) standard is a developing Internet Engineering Task Force (IETF) standard. The 802.15.4e will be the de-facto link-layer technique for the emerging 6TiSCH standard, which provides IPv6 networking capabilities for low power wireless networks. The 802.15.4e standard does not specify how a schedule is built. Therefore, a number of techniques and algorithms have been proposed for scheduling in 6TiSCH wireless networks.
Scheduling in 6TiSCH wireless networks can occur in both centralised and decentralised/distributed ways; however, centralised approaches are only suited to fairly static (in terms of traffic and topology) networks. Further, the scalability of centralised scheduling becomes challenging in networks with higher node density. Therefore, from a practical perspective, decentralised/distributed scheduling techniques are much more attractive.
There is therefore a need for improved distributed scheduling mechanisms for multi-hop networks.